typeof "John"; // returns "string"
typeof 21; // returns "number"
typeof true; // returns "boolean"

Number() - converts a variable or a value into a number
parseInt() - converts into an integer
parseFloat() - converts into a floating point number 

String() - can convert numbers into strings 
.toString() - does the same

Boolean("hello"); // true - converts into Booleans 
Boolean(0); // false 
Boolean(""); // false